I have a copyright 1898 edition of John Broadus' On the Preparation & Delivery of Sermons. The first edition was printed in 1870. Broadus was professor of homiletics at SBTS in Louisville, KY and died in 1895. Here he lists and explains "helps" concerning freshness in preaching (pgs 146-149). "The basis of preaching and the truth preached must ever be the same. Yet there is a freshness in the treatment of old truths, and in discoursing on the unchangeable basis of God's Word, that is eminently desirable and should be maintained though life."

1. Study the Scriptures. Earnest and continued study both of the Bible in general, and of each text in particular, will greatly enhance and sustain a preacher's freshness. Let him...seek not mere novelties and fancies in interpretation, but the exact meaning of the inspired Word. No matter how often he has studied the book or the text before, let him keep on, and new thoughts will be suggested. A man cannot fail to keep fresh in his preaching who continues through life really and properly to study the Word of God.

2. Study Theology. Keep in touch with the great books, both general treatises and special discussions, on Systematic Theology. Doctrine -- real doctrine -- is needed as a novelty in much of the preaching of our times. By all means should a man reflect profoundly upon the commonplaces of religious truth. Vinet well said that the basis of eloquence is commonplace; and another has remarked that the pulpit often "makes the mistake of giving us common thoughts about deep things, when what we need would be deep thoughts about common things." We get these deep thoughts about common things only by penetrating and persevering reflection.

3. Study occasions. Here, again, we should not be directly seeking freshness in itself, but the reality of things. The best freshness is found by simply seeking real adaptation to the real occasion. Study the general condition of the congregation; reflect upon the special occurrences of religious interest, and upon any of secular interest that may furnish illustration or call for passing application or remark. Whenever you repeat a sermon on a new occasion adjust it in your study beforehand to the new conditions. A sermon that suits equally well all occasions does not thoroughly suit any one of them. This adaptation to circumstances often depends upon apparently slight matters.

4. Study individual cases. Physicians and lawyers may set us here a valuable lesson. The wise preacher will know people individually, and how to apply the truth to their special needs. He may thus have the advantage of the Romish confessional without its grave objections. Sometimes a hint in conversation will be a rich germ of suggestion. No man can keep fresh in the pulpit without keeping up both spiritual and social contact with people.

5. Study the age in which we live. Let the preacher strive to understand the strength and the weakness of the age -- its healthy tendencies and its diseases -- its illusions and its well-founded hopes. Particularly should he endeavor to discover and proclaim the true relations of Christianity to the age -- what it needs from Christianity, and what Christianity needs from it. Its currents of thought and sentiment, religious and irreligious -- its difficulties and yearnings -- its movements and changes -- demand the thoughtful attention of the gospel preacher. Yet he should let the fruits of his study and reflection appear not so much in formal discussions through set discourses, as in apt allusion and application here and there in his ordinary sermons. Thus he may be constantly showing how truly Christianity meets all real human wants; and thus he may restrain and fortify his hearers without perplexing them with plausible errors. Excellence in preaching, like the truly excellent in literature and art, must either take hold of things present, even transient things, and penetrate though them to permanent eternal principles; or, if it begins with general principles, it must always bring them to bear upon living characters and actual wants.

6. Study yourself. A man should continue through life to learn from his mistakes. Certainly the young preacher should do this, and even more imperatively the elder. Never fall into stereotyped methods of treating your subjects; cherish and cultivate a restless longing to preach better, and try frequent experiments in preaching differently. There is among preachers a deal of latent power which never gets itself developed. By all means should the inventive faculty be kept healthy and active. Some one has said, "Attention is the mother of invention." Fasten the mind on your subject by resolute effort of the will, and compel yourself to the task of analysis and association of ideas, which are the principal parts of invention. This may also be greatly stimulated by reading and conversation. And let us remember that our very best, our richest invention, is not achieved in preparing next Sunday's sermons, but in general reading, conversation, reflection, when the mind is quiet, throws off its accustomed burdens, and springs up elastic. All the labor and thought thus bestowed in cultivating and maintaining freshness will be richly repaid many times over in sustained power and usefulness in the pulpit.